Intrinsic and hysteresis properties of FePt nanoparticles

This comprehensive study examines the effect of particle size and atomic ordering on the intrinsic and hysteresis properties of FePt nanoparticles embedded in a carbon matrix formed by annealing sputtered FePt/C multilayer precursors. Structural studies show a transformation from the magnetically soft to the tetragonal FePt phase dependent on the annealing conditions. The magnetic properties scale as a function of particle size. The coercivity depends, in part, on the vol % of carbon and develops with annealing as a result of increased atomic ordering. Under the right conditions a high coercivity of 34 kOe has been achieved. Remanence curves show a variation of interparticles interactions from exchange to magnetostatic with increasing vol % carbon. Time dependent measurements indicate a decrease of the activation volume converging to the actual particle size (determined by TEM) as the carbon content is increased. The potential for future magnetic recording media is discussed.